232 The Molluscan Family Planorbidae 



cus. The lower surface has a somewhat pinched appearance, with an 

 indistinct, impressed Hne bordering the periphery. Sculpture of coarse 

 growth lines radiating from the periphery. At regular intervals there are 

 larger rib-like projections, with four to six of the smaller ribs between. 

 All the ribs extend into the spire cavity, which is deep. The sculpture is 

 more conspicuous on the base of the shell. The umbilical (upper) side has 

 the fine riblets more regularly spaced without the larger ones. This sculp- 

 ture is most apparent on the large holotype specimen. There are likewise 

 fine, impressed spiral lines. Aperture triangular, wider than high. Columella 

 almost vertical. Lip thickened by callus, which includes the columellar and 

 parietal walls. The right side of the aperture is acute and pinched. 

 Shell Greater Lesser Aperture Aperture 



Height Diameter Diameter Height Diameter 



1.1 1.6 Holotvpe 



1.0 1.5 Paratvpe 



0.9 0.9 Paratype 



Type Locality. Caloosahatchie River, Florida. 



Type Material. Pliocene fossils, collected by W. H. Dall, deposited in 

 the United States National Museum, Accession no. 112556. Holotype 

 figured on plate 140 as Fig. 22; paratypes as figs. 23, 24. 



Menetus dalli differs from alabamensis in the former's smaller and 

 deeper spire depression and its heavier growth lines forming riblets. It was 

 identified by Dall (after whom the new species is named) as exacuous. It 

 was associated with dilntatus and alabamensis aims. 



Menetus dilatatus floridensis, New Variety 

 Plate 123, figs. 20-22 



Shell small, of three whorls, slowly increasing in diameter. Color light 

 horn. Body whorl forms a rounded obtuse angle as in dilatatus. Base flatly 

 rounded. Spire depression wide, shallow, showing all of the whorls. Sculp- 

 ture of fine growth lines crossed by fine spiral lines. Aperture rounded, 

 not flaring. Outer lip thin. No callus on parietal wall. 



Shell Greater Lesser Aperture Aperture 



Height Diameter Diameter Height Diameter 



0.8 1.0 Holotype 



0.7 . S Paratype 



0.7 0.7 Paratype 



Type Locality. St. Johns River, Palatka, Florida. 



Type Material. Collected by W. H. Dall. Deposited in the United States 

 National Museum, Accession no. 37585. Holotype shown on plate 123 as 

 fig. 20; paratypes as figs. 21 and 22. 



Menetus dilatatus jioridensis differs from typical dilatatus in the fact 

 that the new variety has a smaller aperture which is rounded, not flaring; 

 has rounded body whorl, without trace of angulation; and has wider, shal- 

 lower spire depression, showing all of the whorls. 



Menetus lahiatus. New Species 

 Plate 121, figs. 9-11 



Whorls three, rounded. Spire flattened, apex sunken. Base rounded, umbili- 

 cus broad and shallow, one-sixth the diameter of the shell. Whorls and 



